It is known that reinforcing fillers, such as carbon black and silica greatly improve the strength and fatigue properties of elastomeric compounds. It is also known that chemical interaction occurs between the elastomer and the filler. For example, good interaction between carbon black and highly unsaturated elastomers, such as polybutadiene (BR) and styrene butadiene copolymers (SBR) occurs due to the large number of carbon-carbon double bonds present in these copolymers. Butyl elastomers may have only one tenth, or fewer, of the carbon-carbon double bonds found in BR or SBR, and compounds made from butyl elastomers are known to interact poorly with carbon black. For example, a compound prepared by mixing carbon black with a combination of BR and butyl elastomers results in domains of BR, which contain most of the carbon black, and butyl domains which contain very little carbon black. It is also known that butyl compounds have poor abrasion resistance.
Canadian Patent Application 2,293,149 discloses that it is possible to produce filled butyl elastomer compositions with improved properties by combining halobutyl elastomers with silica and specific silanes. These silanes act as dispersing and bonding agents between the halogenated butyl elastomer and the filler. However, one disadvantage of the use of silanes is the evolution of alcohol during the process of manufacture and potentially during the use of the manufactured article produced by this process. Additionally, silanes significantly increase the cost of the resulting manufactured article.
Canadian Patent Application 2,339,080 discloses a process for preparing compositions containing halobutyl elastomers and organic compounds containing at least one basic nitrogen-containing group and at least one hydroxyl group, in which there is enhanced interaction between the elastomer and a filler, especially a mineral filler. Of interest were compounds containing primary amine and hydroxyl groups such as ethanolamine. While solving the problem of enhancing the interaction between elastomer and filler, the compositions have to be processed carefully to prevent any undesirable scorch of the composition. Those skilled in the art understand the term “scorch” to mean premature crosslinking of the composition during processing.
Canadian Patent Application 2,412,709 discloses a process for preparing compositions containing halobutyl elastomers, organic compounds containing at least one basic nitrogen-containing group and at least one hydroxyl group, and hydrated metal halogens. The process provides enhanced interaction between the elastomer and mineral fillers, while at the same time providing improved scorch safety. However, the traction and wear properties of the composition could still be improved upon.
Canadian Patent Application 2,418,822 discloses a process for preparing a filled halobutyl elastomer, which comprises mixing a halobutyl elastomer with at least one mineral filler that has been reacted with at least one organic compound containing at least one basic nitrogen-containing group and at least one hydroxyl group and, optionally, with at least one silazane compound. The process provides enhanced interaction between the elastomer and mineral fillers, while at the same time providing improved scorch safety. However, the traction and wear properties of the composition could still be improved upon.
Canadian patent application 2,564,446 discloses the use of a two component mixed modifier system in rubber compounds. The mixed modifier system comprises a combination of a silane modifier with a compound containing at least one hydroxyl group and a functional group containing a basic amino group. This two component modifier system was shown to have advantages over either class of modifiers used individually. The compounds exhibited improved traction properties but these materials exhibited high compound Mooney and poor processability.
In a recent publication by Parent et al (Macromolecules, 37 (2004) 7477-7483; Polymer, 45 (2004) 8091-8096.) the use of triphenyl phosphine was shown to generate a butyl ‘ionomer’ upon mixing in the solid state. These phosphonium bromide ionomer derivatives of an isobutylene-based elastomer (IIR-PPh3Br) show improved ionic interactions with ion-exchanged montmorillonite clays leading to improved barrier properties and mechanical reinforcement. Similar increased polymer-filler interactions were observed between the ionomer and precipitated silica, resulting in reduced filler agglomeration and higher degrees of filler reinforcement.
However, there is still a need for rubber compounds useful in tire treads that exhibit improved processability, wet traction, rolling resistance and/or wear resistance.